246 DR. W. N. F. WOODLAND ON THE 



Gobius niger (PI. III. fig. 22 ; PI. IV. figs. 23-32, 34; PI. V. fig. 33). 



Fig. 22 ( X 1). Appearance of the " red body " in the ventral bladder wall. 



23 (X 16). Semi-diagrammatic transverse section anterior to the "red bodj'." 



A. and V., the initial artery and vein which form the rete mirabile ; 

 E.G., pancreas masses ; O.L., outermost layer of the bladder wall; 

 G.E., glandular epithelium lining bladder cavity. It will be 

 noticed that the vessels and pancreas lie outside the bladder wall. 



24 (X 16). More posterior section. The initial artery and vein have subdivided 



to a small extent. The outermost layer of the bladder wall has 

 become broken through by the arteries, veins and masses of 

 pancreas. 



25 (X 16). The arteries and veins, intermingled with masses of the pancreas, 



are rapidly subdividing to form the rete mirabile and the whole 

 mass is now practically situated inside the bladder wall. 



26 (X 16). The rete mirabile (R.M.) has now commenced to supply the 



glandular epithelium (G.E.) and is situated wholly inside the 

 bladder wall, i. e. internal to the outermost layer (O.L.). E.G., 

 portion of the pancreas remaining external to the bladder. 



27 (X 330). Three folds of the bladder glandular epithelium in transverse 



section. C.R.M., minute capillaries of the rete mirabile; EU., 

 gas-bubble; ICC, intracellular capillary. 



28 (X 800). Gas gland cell with intracellular capillary (ICC). Note the 



striped darkened zone of cytoplasm next the capillary. 



29 (X 800). Gas gland cells with inter- and intracellular capillaries (ICC). 



30 (X 800). Gas gland cell with intracellular lumen in transverse section. 



Intracellular ducts, when thus seen, are not always easy to 

 distinguish from bubbles. 



31 (X 800). Gas gland cell with intercellular lumen (INT.CL.) in transverse 



section. 



32 (X 1000). Transverse section through anterior end of rete mirabile, showing 



the curious endothelium (END.) of the arteries in this region and 

 the large amount of erythrocyte-disintegration granular matter 

 contained in the veins. The arteries (A.) are here distinguishable 

 from the veins (V.) by their smaller size, by their thicker walls, by 

 possessing the curious endothelium and by being practically free 

 from granular matter (S.G.). 



33 (X 800). A diict of the pancreas in longitudinal section. The numerous 



nuclei and the syncytial character of the wall are noticeable. A 

 large amount of granular secretion-matter is present in the duct. 



34 (X 800). A duct of the pancreas in transverse section. 



Gobius minutus (PI. V. fig. 35). 



Fig. 35 (X 1000). Portion of the folded epithelium of the gas gland in a very active 

 condition. Bubbles are seen being produced (usually near the 

 nuclei) in the interiors of most of the cells, others are being 

 extruded from the cells and one is shown Ij'ing freely in the 

 bladder cavity. The large amount of granular matter lying in the 

 bladder lumen external to the gas gland cells which has resulted 

 from the bursting of extruded bubbles is noticeable. 



SipJioiiostoma typlile {rondeletii) (PI. V. fig. 36). 



Fig. 36 ( X 1000) . In addition to the erythroc3'tes there are shown three of the 

 curious " white " corpuscles which are so striking in appearance in 

 this fish, the cytoplasm being very dense. Tliese corpuscles are 

 numerous. 



FeristetJms catapliractiis {Peristedion cataphractum) (PI. V'. figs. 37-41). 



Fig. 37 (X 1). Appearance of " red body" in ventral wall of bladder. 



38 (X 16). Semi-diagrammatic transverse section across the anterior end of the 



"red body" (see A-E, text-fig. 57, p. 202). S.E., squamous 



epithelium lining the greater part of the bladder; G.E., glandular 



epithelium; R.M., rete mirabile. 

 Figs. 39-41 (X 1600). Cells of the gas gland showing formation of bubbles in 



cytoplasm. 



